District Heating Boiler Station

(Peak Load Boiler Station)

A key component of the Lerwick District Heating Scheme in Shetland, the District Heating Boiler Station (also known as the Peak Load Boiler Station) is located on the Marina Business Park at Gremista, next to Lerwick Power Station, 1¼ miles (2 km) northwest of the town centre. Opened with the heating scheme in 1998, the Boiler Station now comprises a pumping system and three oil-fired boilers which provide a backup to the Energy Recovery Plant at Green Head, which creates energy from waste. Heating is provided to around 1100 customers by circulating hot water through a 19-mile (30-km) long pipe-network laid around Lerwick. Most customers lie to the south (townward side) of the District Heating Boiler Station. The Boiler Station powers the District Heating Scheme when the Energy Recovery Plant is closed for maintenance and also augments the output from the Energy Recovery Plant at times of high demand or in particularly cold weather. Built with two boilers (2 MW and 6.5 MW), another 6.5 MW boiler was installed in 2008 to give a total capacity of 15 MW. Using customers' formerly-independent boiler systems as additional backup, gives a further 6 MW of capacity spread around Lerwick if required. The Boiler Station also incorporates a thermal storage tank, added in 2006. Reaching a temperature of 110°C, this absorbs heat generated by the Energy Recovery Plant overnight and emits this during the day, effectively smoothing out demand. The construction of this 300 cu. m (10,594 cu. foot) tank, 19m (62 feet) in height and 4.5m (14¾ feet) in diameter, was justified by the cost savings of not having to run the boilers to the same extent to meet peak loads.

The scheme is set to expand through greater use of stored energy. Scottish and Southern Energy will build three wind turbines, each rated at 2.3 MW, to be located at Rova Head. These will feed into Shetland's electricity network via Lerwick Power Station, but excess energy overnight will be used to run a large immersion heater fitted inside a new a 135 MWh thermal storage tank located in the District Heating Boiler Station. Thus additional capacity will be created for the district heating system, allowing further customers to be connected and completely removing the need to burn oil at peak times. Given that the demand for heat rises on windy days, due to the wind-chill effect, the wind turbines should be operating at full capacity at the times of greatest demand. Equally, the thermal store will give several days capacity at times of no wind. This will represent the first wind-to-heat scheme in the UK and is expected to be operational by 2015.

The District Heating Scheme is run by Shetland Heat Energy and Power Ltd., who has its offices adjacent to the Boiler Station.

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